1. Field of the Invention
The present invention relates to a refrigeration cycle apparatus for heating the interior of a vehicular passenger compartment, more particularly it relates to a vehicular use air-conditioning system provided with a refrigeration cycle apparatus designed to guide the high temperature, high pressure gas phase refrigerant discharged from a refrigerant compressor into a refrigerant evaporator and heat the air flowing through a duct at that refrigerant evaporator.
2. Description of the Related Art
In the past, the general vehicular use heating system used has been a hot water type heating system which guides the coolant water which had been used for cooling the engine into a heater core in a duct to heat the air flowing through the duct by that heater core and thereby heat the interior of the passenger compartment. This hot water type heating system, however, suffered from the problem of a remarkably insufficient heating capacity when just starting up the engine and activating the hot water heating system, that is, when the hot water heating system is just starting up, when the temperature of the outside air was low and the temperature of the used cooling water was consequently low.
To solve the above problem, for example, Japanese Unexamined Patent Publication (Kokai) No. 5-223357 has proposed a vehicular use air conditioning system (related art) provided with a refrigeration cycle apparatus (auxiliary heating system) designed to augment the heating capacity of the heater core by leading the high temperature, high pressure gas phase refrigerant (hot gas) discharged from the compressor of the refrigeration cycle apparatus through a pressure reducing apparatus to a refrigerant evaporator and heat the air flowing through the duct at that refrigerant evaporator. Note that the compressor was an engine-driven compressor driven by the engine through an electromagnetic clutch.
During the heating operation, when the temperature of the cooling water is over a predetermined temperature, the heating capacity of the heater core of the hot water type heating system is sufficiently high, so the compressor is turned off and the auxiliary heating system is deactivated. Further, when the temperature of the cooling water is lower than a predetermined temperature, the heating capacity of the heater core of the hot water type heating system is insufficient, so the compressor is turned on to activate the auxiliary heating system.
Further, when the discharge pressure from the compressor is higher than a predetermined pressure, the load on the compressor is too high, so the compressor is turned off to deactivate the auxiliary heating system and protect the refrigeration cycle apparatus. Further, when the discharge pressure from the compressor is less than a predetermined pressure, the compressor is turned on to activate the auxiliary heating system.
Further, in the apparatus of this related art, an accumulator is provided between the refrigerant evaporator outlet and the compressor suction side to separate the gas and liquid phases of the refrigerant and lead the gas phase refrigerant for use elsewhere so as to prevent the suction of liquid phase refrigerant to the compressor and therefore avoid an adverse effect on the life of the compressor by liquid compression.
In this refrigeration cycle apparatus of the related art, however, if the heating operation at the hot gas heater circuit is continued for a predetermined time (for example, about 30 minutes), both the high-side pressure and the low-side pressure of the refrigeration cycle apparatus became higher than during the cooling operation using the ordinary refrigeration cycle circuit. For example, the high-side pressure of the refrigeration cycle apparatus would become 20 to 25 kg/cm.sup.2 during a heating operation (operation by a hot gas heater circuit) and 13 to 15 kg/cm.sup.2 at a cooling operation (operation by a refrigeration cycle circuit). Further, the low-side pressure of the refrigeration cycle apparatus would become 4 to 5 kg/cm.sup.2 during a heating operation and 1 to 2 kg/cm.sup.2 during a cooling operation.
Further, during a heating operation by the hot gas heater circuit, compared with the cooling operation at the normal refrigeration cycle circuit, as mentioned above, both the high-side pressure and the low-side pressure of the refrigeration cycle apparatus would become higher and the torque fluctuation would become greater when turning the compressor from the on state to the off state. Therefore, when the compressor was turned from the on state to the off state during operation of the vehicle, the rotational speed of the engine belt driving the compressor would fluctuate tremendously and therefore the problem would arise of deterioration in both the power performance and driveability of the vehicle.
It may therefore be considered to control the capacity and control the pressure without frequently turning the compressor on and off by changing the compressor to a cooler use variable volume type compressor such as used in the past. This conventional cooler use variable volume type compressor, however, is designed to reduce the discharge volume from the compressor the lower the suction pressure to the compressor.
When installing such a cooler use variable volume type compressor in a hot gas heater circuit for a heating operation, the larger the heating load, that is, the lower the temperature of the air sucked into the evaporator, the lower the temperature and the pressure of the refrigerant used for heat exchange with the air in the evaporator. Due to this, since the discharge volume from the compressor becomes smaller due to the variable volume control of the compressor, the flow of high temperature refrigerant into the evaporator also becomes smaller and therefore the problem arises that the auxiliary heating performance, that is, the performance in assisting the heating capacity of the heater core, is no longer sufficiently manifested.
Further, when installing a cooler use variable volume type compressor into the hot gas heater circuit for a heating operation, when the heating capacity is small, that is, when the temperature of the air sucked into the evaporator is high, the temperature and the pressure of the refrigerant used for the heat exchange with the air in the evaporator become high. Due to this, since the discharge volume from the compressor becomes larger due to the variable volume control of the compressor, the discharge pressure from the compressor becomes larger.
If the high-side pressure of the refrigeration cycle apparatus were to rise to an abnormally high pressure temperature (for example, 27 kg/cm.sup.2), the components of the cycle such as the refrigerant piping would malfunction or break. Further, even if the heating load is small, as explained above, if the high-side pressure of the refrigeration cycle apparatus reaches 25 kg/cm.sup.2, the flow of the high pressure refrigerant into the evaporator will also become large, so the problem will arise of an excessive auxiliary heating capacity for assisting the heating capacity of the heater core.
Further, in the above apparatus of the related art, while no reference was made to the specific configuration of the apparatus, as is generally known, a calibrated orifice passage for recovering the fine oil is provided near the bottom of the inside of the accumulator. The liquid refrigerant (including the lubrication oil) near the bottom of the inside of the accumulator is designed to be drawn in from this calibrated orifice passage so as to eliminate the insufficient lubrication of the compressor and protect the compressor life.
The present inventors engaged in actual experiments and studies on how far the opening of the calibrated orifice passage (the passage diameter, also called the bleed port diameter) should be set and found that the following problem arises. That is, when the opening degree of the calibrated orifice passage is enlarged to the maximum value (for example, .o slashed.2.5) at the time of heating operation in the winter (operation by hot gas heater circuit), the amount of suction of liquid refrigerant into the compressor through the calibrated orifice passage increases, so the amount of compression work of the compressor increases and it is possible to increase the heating capacity as well. On the other hand, since the amount of suction of the liquid refrigerant at the time of a cooling operation in the summer also increases, the amount of oil circulating in the cycle also increases which invites a reduction in the cooling capacity and an increase in the power consumption of the compressor.
Therefore, if the diameter of the calibrated orifice passage is reduced to the optimal value for a cooling operation in the summer (for example, .o slashed.1.2), the amount of suction of liquid refrigerant during a cooling operation in the summer will fall and the cooling capacity will be improved so it would be possible to reduce the power consumption of the compressor, but at the time of a heating operation in the winter, the amount of compression work of the compressor will fall so the heating capacity will fall and become insufficient.